Conventional wind turbine towers typically include a tubular pole or a lattice structure to support a wind turbine at a considerable height to capture wind energy. The tubular pole configuration is relatively more simple and easier to assemble than the lattice structure. However, tubular poles use more steel than the lattice structure, resulting in a cost disadvantage with rising prices of steel.
Thus, lattice tower structures can have potential as an alternative to the tubular poles, especially for higher hub height applications and for wind turbines located in wind farms having challenging logistic requirements. For example, transporting the tubular tower sections to the site can be challenging because the sections can be twenty plus meters long and over four meters in diameter. As such, in some instances, a dedicated road is needed, but may not be possible. Accordingly, lattice tower structures may be utilized since they do not experience the same transportation issues as tubular towers.
For example, FIGS. 1 and 2 illustrate perspective views of a plurality of wind turbines 40 having a lattice tower structure 48 known in the art. As shown, the wind turbines 40 include a plurality of blades 42 mounted to a rotor hub 44, which in turn is rotationally supported by power generation components housed within a nacelle 46, as is well known in the art. The nacelle 46 is supported at the top of the lattice tower structure 48, which in the illustrated embodiments is formed by legs 50, horizontal braces 54, and diagonal braces 52. The legs 50 are typically angle iron members or pipe members, and the braces 52, 54 are typically angle iron members. The vertical supports (legs 50) are typically provided for bending loads, whereas the cross support-members 52, 54 connect the legs 50 and are typically provided for torsional loads. These lattice frame tower structures 48 are also referred to in the art as “space frame” towers. The lattice tower structure 48 may be fabricated in sections and erected at the wind turbine site. FIG. 3 is a more detailed view of the structural members of the lattice structure tower 48, and particularly illustrates the connection locations between the braces 52, 54 and the legs 50, as well as between aligned sections of the legs 50. Typically, a plurality of bolt connections 60 are utilized at these various connection locations.
Certain modern wind turbines may have a hybrid configuration including both steel tubular portions and a lattice frame structure. Such hybrid towers are particularly advantageous to accommodate higher hub heights. Previous hybrid towers, however, typically include a plurality of welded joints, particularly at the transition between the steel tubular portion and the lattice frame structure.
Accordingly, an improved hybrid tubular lattice tower assembly for a wind turbine that addresses the aforementioned problems would be desired in the art.